1. Field of the Invention
The present invention relates to an image distortion correction of an image displayer, and more particularly, to an apparatus and a method for correcting a distorted image which is capable of correcting an optical distortion of an image and misconvergence by prewarping an inputted image without using a convergence yoke, and an image displayer using the same.
2. Description of the Background Art
These days, a television set is a requite item of electronic appliances. Thus, as the standard of living is improved, a high quality of television set is increasingly demanded. In order to meet the demands, there have been developed high quality television sets, one of which is a projection TV in which an image focused on a red, a green and a blue cathode ray tubes is enlarged, the enlarged image is reflected on a mirror and the image reflected on the mirror is projected on a large screen, so that viewers can watch an enlarged TV image.
FIG. 1A is a view showing a construction of a general projection TV 100, which includes a red, a green and a blue cathode ray tubes (CRTs) 3, 4 and 5, a lens 6 for enlarging images outputted from the CRTs 3, 4 and 5, a mirror 1 for making incident and reflecting the images, and a screen 2 for displayed the images reflected and enlarged from the mirror 1.
Images outputted from the CRTs 3, 4 and 5 is transmitted through the lenses 6 respectively attached to the CRTs 3, 4 and 5 and reflected on the mirror 6 to reach the screen 2 of the projection TV 100, thereby being displayed as an enlarged image.
However, since the image displayed on the screen of the projection TV 100 is influenced by the position and angle of the plural CRTs and the optical elements, an optical distortion is inevitably created for the image.
FIG. 1B is a view showing trajectories of images displayed on the screen 2 of FIG. 1A. Depending on the relations between positions of the CRTs 3, 4 and 5 and the position of the mirror, the red, the green and the blue image trajectories do not agree to each other, and the image trajectories are distorted or angulated.
The optical distortion has a non-linear characteristic due to the several factors such as the position of the CRTs and the mirror, a magnifying power of the lens and a magnetic field. The optical distortion is divided into a pincushion distortion caused by the CRT and the lens as shown in FIG. 2A, and a keystone distortion caused due to the reflection of the mirror as shown in FIG. 2B.
The pincushion distortion is a distortion generated as the proceeding distance of electron beams generated and outputted from the CRT (specifically, an electron gun) is away from the center of the CRT The degree of the distortion becomes severe as it goes away from the center of the CRT.
Meanwhile, the keystone distortion is that an image is reflected on different spots of a mirror according to lenses and the reflection path from the mirror to the screen is different. For example, a rectangular-shaped original image is distorted to a trapezoidal image. The key stone distortion is evenly generated on the whole image displayed on the screen.
Especially, when the red, the green and the blue CRTs are arranged, as shown in FIG. 1B, the electron beams outputted from the blue CRT and the red CRT are made diagonally incident on the mirror, so that a keystone distortion occurs more severely, compared with the electron beam outputted from the green CRT which is made directly incident on the mirror.
Accordingly, in case of the projection TV, since the three CRTs are arranged side by side, rather than being installed at the same position, the pincushion distortion and the keystone distortion degree are changed according to the right, left, upper and lower portions of the image. In addition, the projection TV has a problem of misconvergence in that since the three color signals are not projected on the same spot, a desired color image is hardly obtained. In this respect, the misconvergence occurs together with the optical distortion.
FIG. 3 is a schematic block diagram of an apparatus for correcting an image distortion of an image displayer in accordance with a conventional art.
As shown in the drawing, the apparatus for correcting an image distortion includes an image processor 11 for processing a signal received from an external source and outputting an image signal and a horizontal and a vertical synchronous signals; a CRT 12 for receiving the image signal and generating an electron beam; a horizontal and a vertical deflection unit 16 for receiving the horizontal and the vertical synchronous signal and outputting a convergence control signal and a horizontal and a vertical deflection control signals; a deflection yoke (DY) 14 attached to the CRT 12 for flowing current for horizontal and vertical deflection of an electron beam according to the horizontal and the vertical deflection control signals; a correction wave form generator 17 for receiving the convergence control signal and outputting a convergence correction signal; a conversion amplifier 18 for inputting the correction signal and outputting an amplified correction signal; a convergence yoke (CY) 13 attached to the CRT 12 for flowing current so as not to spread electron beams outputted from the CRT; and an optical system 15 for making incident the electron beams outputted from the CRT 12 and displaying an image.
According to the apparatus for correcting a distortion of an image in accordance with the conventional art, a lump of coils such as the convergence yoke or the deflection yoke are installed at the CRT, and an appropriate correction current of a horizontal and a vertical directions is applied to the convergence yoke (the intensity of the current is controlled) to thereby control a path of the electron beam, so that the optical distortion is corrected and the convergence of the color signal is controlled.
That is, in order to control the electron beams outputted from the RGB CRTs, a deflection controlling current is produced for each RGB CRT lens. And then, the current is greatly amplified and applied to the convergence yoke, by which the electron beam landed on the screen is controlled to be converted on the same spot, not being spread.
However, in the distortion correcting apparatus, the image distortion generated in the projection TV has a non-linear characteristic. Thus, in order to obtain a current to be applied to the convergence yoke, a control signal having a non-linearity is to be generated, for which an amplifier for amplifying the current is to be provided and a complex and difficult operation algorithm should be implemented.
In addition, in case of the conventional projection TV in which the distortion is corrected by varying a landing of the electron beam according to the controlling of the current, even though the distortion is corrected by distortion correcting apparatuses before coming out to the market, as time goes by, the distortion correcting apparatuses are influenced by parts degradation, a temperature change and an earth magnetic field. Thus, a distortion phenomenon occurs, deteriorating its performance. In addition. Once the distortion in the projection TV occurs, it is not possibly corrected.